Polyvinyl chloride (PVC) compositions are commonly used as packaging materials for cosmetics, pharmaceuticals, foods and health care products. Polyvinyl chloride is preferentially selected for these packaging applications due to its low cost, clarity and ease of processing. In some packaging applications it is very desirable that plastic materials exhibit a very high gas impermeability. The gas barrier properties of PVC compositions are adequate for some applications but require improvement for the protection of extremely oxygen-sensitive materials.
The gas barrier properties of PVC may be improved by chemical or physical modification, or by the addition of a filler or a protective coating. A preferred approach to improving the gas barrier properties of PVC is by blending with barrier materials. Blends in general do not always have the additive properties of the two components. The properties of the blend in many instances are worse than the properties of the pure components. Therefore, blending a barrier polymer with PVC polymers does not necessarily lead to a composite with improved gas impermeability relative to PVC. This invention describes the blending of olefinic nitrile barrier polymers with vinyl halide polymers to produce a blend whose barrier properties are additive.
The olefinic nitrile polymers themselves are used to form films and containers which are characterized as having improved oxygen and carbon dioxide gas barrier properties. These high nitrile compositions are available from a variety of sources and are described in various patents. For example, U.S. Pat. No. 3,974,239 describes impact-resistant polymers which have low permeability to gases and vapors. The polymers are prepared by polymerizing an olefinic nitrile such as acrylonitrile with an acrylic ester and a conjugated diene which may be either butadiene or isoprene. These compositions are reported to be improvements over the compositions obtained by the process described in U.S. Pat. Nos. 3,426,102 and 3,586,737 which describe the preparation of impact-resistant vapor and gas barrier resins composed of an olefinic nitrile such as acrylonitrile, optionally an acrylic ester, and a preformed diene rubber wherein the preformed diene rubber is present during the resin polymerization reaction.
U.S. Pat. No. 3,891,722 describes impact-resistant polymers having low permeability to gases and vapors which are obtained by polymerizing an olefinic nitrile such as acrylonitrile, an olefinic ester such as ethyl acrylate or a monoolefin such as isobutylene in the presence of a diene rubber. These compositions contain at least 50% by weight of the olefinic nitrile.
U.S. Pat. No. 4,003,963 describes vinyl chloride polymer barrier packaging compositions which are blends of vinyl chloride polymers containing no carboxyl groups and about 20 to 30% by weight of an ethylene-vinyl alcohol copolymer containing greater than 50 mole percent of vinyl alcohol. The compositions are reported to have enhanced resistance to gas permeability and moisture vapor transmission.
British Patent No. 1,279,745 also describes polymeric compositions which have low permeability to gases and which are impact-resistant. The compositions described in the British patent are composed of a conjugated diene monomer, an olefinic nitrile and, optionally, an ester of an olefinically unsaturated carboxylic acid or a monoolefin.
Commercially available "high nitrile" compositions having improved gas barrier properties are available from, for example, BP Chemicals International, Specialties Division, under the general trade designations "BAREX.RTM.210 " and "BAREX-218". BAREX-210 is believed to be a polymeric material composed of approximately 90% of a copolymer of about 70% acrylonitrile and 30% methyl acrylate, and 10% of butadiene. Barex 218 is composed of 82% of the copolymer and 18% Of butadiene.
Nitrile barrier polymers obtained by interpolymerization of a mixture of acrylonitrile, vinylidene chloride and acrylate monomers are described in U.S. Pat. No. 3,832,335. The polymers are reported to be useful in preparing films and containers having improved oxygen barrier properties.
Although compositions of the types described above exhibit reduced gas permeability, there continues to be a need for polyvinyl chloride (PVC) compositions having even lower gas permeability and/or polyvinyl chloride compositions having low permeabilities to not one but a number of different gases. However, it often occurs that the compositions being combined with the PVC are incompatible which may result in a hazy or non-transparent composition, or in a composite which when extruded delaminates due to a lack of mechanical integrity of the composition. Also, if the polymers being mixed are incompatible, extrusion of such incompatible polymers often results in the manufacture of a product having a non-homogeneous structure which may or may not exhibit mechanical integrity.
U.S. Pat. No. 4,309,465 describes a process for preparing compositions of thermoplastic materials which are at least partially incompatible. In one example, the extruded thermoplastic composition comprises a continuous phase consisting essentially of polyvinylchloride and a discontinuous phase consisting essentially of polyvinyl alcohol. The compositions are reported to have increased gas impermeability.